In an automated collation technique, one or more ribbons of composite material (also known as composite strands or tows) are laid down on a substrate with a material placement machine. The substrate may be a tool or mandrel, but can also be formed of one or more underlying layers of composite material that have been previously laid down and compacted.
Fiber placement processes typically utilize a heat source to assist in compaction of the plies of composite material at a localized nip point. In particular, the ribbon or tow of composite material and the underlying substrate are heated at the nip point to increase the tack of the resin of the plies while being subjected to compressive forces to ensure adhesion to the substrate. To complete the part, additional strips of composite material can be applied in a side-by-side manner to form layers and can be subjected to localized heat and pressure during the consolidation process.
Unfortunately, manufacturing inconsistencies can occur during the placement of the composite strips onto the underlying composite structure. Such inconsistencies can include tow gaps, overlaps, dropped tows, puckers (i.e., raised regions in a tow), and twists. In addition, foreign objects and debris (FOD), such as resin balls and fuzz balls, can accumulate on a surface of the composite structure which must be detected, identified and eventually removed from the ply surface.
Composite structures fabricated by automated material placement methods typically have specific maximum allowable size requirements for each inconsistency, with these requirements being established by the production program. Production programs also typically set well-defined accept/reject criteria for maximum allowable number of (i.e., density) of inconsistencies per-unit area and maximum allowable cumulative inconsistencies width-per-unit area.
To ensure that the composite laminates fabricated by fiber placement processes satisfy the requirements pertaining to inconsistency size, the structures are typically subjected to a 100% ply-by-ply visual inspection. These inspections are traditionally performed manually during which time the fiber placement machine is stopped and the process of laying materials halted until the inspection and subsequent actions to address or rework the inconsistency, if any, are completed. In the meantime, the fabrication process has been disadvantageously slowed by the manual inspection process and machine downtime associated therewith.
Recently, systems and methods have been developed that are capable of detecting, measuring, and marking individual inconsistencies in the composite structure. Exemplary systems and methods capable of accurately and reliably detecting, measuring and/or marking inconsistencies in a composite structure are disclosed in U.S. Pat. No. 7,171,033, issued Jan. 30, 2007; U.S. Pat. No. 6,871,684 issued Mar. 29, 2005; and U.S. patent application Ser. No. 10/628,691, filed Jul. 28, 2003. The entire disclosures of the above documents are each incorporated herein by reference as if fully set forth herein.
Systems and methods have also been developed which are capable of determining an inconsistency characteristic representative of the composite structure, such as an inconsistency density-per-unit area and/or cumulative inconsistency width-per-unit area. Exemplary systems and methods capable of determining inconsistency characteristics are disclosed in U.S. patent application Ser. No. 10/726,099, filed Dec. 2, 2003, the entire contents of which are incorporated herein by reference as if fully set forth herein.
Systems and methods have also been developed which enable a material placement machine to automatically return to inconsistencies for manually addressing the inconsistencies, and/or that enable the machine to automatically return to and address inconsistencies without operator intervention. Exemplary systems and methods are disclosed in U.S. Pat. No. 7,039,485, issued May 2, 2006, the entire contents of which are incorporated herein by reference as if fully set forth herein.
The above-mentioned inspection systems and methods have worked well for their intended purposes and have reduced unproductive downtime associated with inspection and the actions needed to address the inconsistency in the laminate plies. The inventors hereof have recognized, however, that such systems and methods can be even further improved by providing suitable non-contact marking alternatives to ink-based surface marking systems. By way of background, ink-based marking systems can employ various means, such as inkjet marking, pump-fed felt-tip marker, spring loaded marking pen, among others, to deposit an amount of ink onto the composite structure in those areas where inconsistencies have been detected. With these ink-based marking systems, the ink should be carefully selected to ensure compatibility with the composite substrate and to ensure that the ink doesn't contaminate the composite substrate. The ink should also be low enough in viscosity so that it flows freely through the supply lines and the sprayer nozzle. The solvents used in the ink should also allow the ink to dry quickly enough to carefully select an ink satisfying all of the conditions and can require significant amounts of time and costs.